Conventionally, an ultrasonic diagnosis apparatus creates and displays blood flow information using Doppler signals extracted from ultrasonic reflected waves. The blood flow information created and displayed by the ultrasonic diagnosis apparatus generally includes color Doppler images and Doppler spectrums (Doppler waveforms). The Doppler waveforms are created by time-series plotting of blood flow velocities observed in an area set by an operator as a blood flow velocity observation range. Such a range is set by an operator referring to B-mode images, M-mode images, and color Doppler images. For example, in severity judgment of cardiac valve regurgitation or stenosis, the operator observes a color Doppler image, sets a collection range to an area determined as having regurgitation or a jet stream originating from stenosis, and collects Doppler waveforms using the CW (Continuous Wave) Doppler method or the PW (Pulsed Wave) Doppler method to perform Doppler measurement.
In severity judgment of regurgitation using Doppler measurement, detection of the largest part of a Doppler waveform, that is, the peak blood flow velocity (also referred to as the peak flow velocity) is important. In the CW Doppler method, the S/N (signal/noise) ratio of the largest part of a waveform is generally so low that the boundaries of the waveform tend to be unclear. Furthermore, an area of regurgitation often covers a small range, not a wide range. Thus, a sonographer, who is the operator of the ultrasound diagnostic apparatus, observes a Doppler waveform in real time while changing the way of putting an ultrasonic probe to receive reflected waves from the region of the regurgitation so that the “maximum” peak flow velocity can be obtained and verbally controlling breathing of the patient. The operator performs such an operation while observing and recording Doppler waveforms of multiple heart beats, judging if the “maximum” peak flow velocity has been obtained.
After the operator acknowledged that a Doppler waveform with the “maximum” peak flow velocity had been collected, the operator presses down the “Freeze button”, reads out collected images from the memory, and refers to the collected images. At this point, the operator traces back the collected images to the past as necessary. Thereafter, the operator causes the Doppler waveform determined as of the “maximum” peak flow velocity to be displayed and performs various measurements for severity judgment of regurgitation or stenosis. For example, the operator manually traces the envelope of the Doppler waveform thus displayed, and the ultrasound diagnostic apparatus performs a measurement process based on the trace result. It should be noted that measurement values used for the severity judgment of regurgitation or stenosis include maximum flow velocity that is the “maximum” peak flow velocity, VTI (Velocity Time Integral), and pressure gradient suitably obtained by converting the maximum flow velocity using the Simplified Bernoulli Equation.
In recent years, ultrasound diagnostic apparatuses with functions to automatically trace the envelopes of Doppler waveforms have been developed. Furthermore, this automatic trace function has been used for calculating and outputting the average of measured values such as peak flow velocities at multiple heart beats (three to five heart beats, for example) in the past that include target Doppler waveforms. Although the automatic trace function may be performed by the CW Doppler method, in many cases it is applied to analysis in the PW Doppler method.
However, judgment over the collection of the Doppler waveform with the maximum peak flow velocity depends on the memory of the operator. Thus, in some cases actually, measurement is performed using a Doppler waveform that is not with the maximum peak flow velocity. In such cases, diagnosis accuracy for the severity judgment of regurgitation is decreased. Furthermore, since the recording period is specified for the collection of Doppler waveforms generally, the Doppler waveform with the maximum peak flow velocity cannot be displayed in some cases where the recording period expires. In such cases, recollection of Doppler waveforms becomes necessary, lengthening the examination time.